Hydraulic shock absorber



3 Sheets-Sheet l N. S. FOCHT VHYDRAULIC SHOCK ABSORBEB.

March 29, 1949.

Filed Nov. 29; 194e March 29, 1949. N. s. FocHT HYDRAULIC SHOCK ABSORBER 5 Sheets-Sheet 2 Filed NOV. 29. 1946 me/WM Doi# @www March 29, 1949. N. s. FOCHT HYDRAULIC sHocK ABsoRBER 3 Sheets-Sheet 3 Filed Nov. 29. 1946 Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE HYDRAULIC SHOCK ABSORBER Nevin S. Focht, Syracuse, N. Y.

Application November 29, 1946, Serial No. 712,935

(Cl. 18S-88) 5 Claims. 1

This invention relates to shock absorbers, and has particular reference to improvements in hydraulic shock absorbers of the cylinder and piston or strut type as described and claimed, for example, in my prior Patents Nos. 2,144,583,

2,240,644, 2,342,729, 2,403,648 and 2,409,349.

Assuming use of the present shock absorber between the body and an axle of a vehicle wherein the body is yieldably supported upon the axle through the instrumentality of springs, one special and important object of the present invention is to provide improved valve means for so controlling flow of liquid through the piston of the shock absorber as to cause the shock absorber effectively to snub rebound action of the vehicle springs following their above normal compression, and yet to permit the shock absorber to distend substantially freely from its normal position to allow the vehicle wheels to drop substantially freely into roadway holes, all to the end of imparting smooth riding qualities to the vehicle.

According to the present invention, the piston of the shock absorber is provided with a metering pin to regulate flow of liquid through the piston for the purpose of snubbing rebound action of the vehicle springs following compression shocks imparted to the shock absorber and said springs. The metering pin is actuated to a set" position by the compression shock, and is movable from its set position during the rebound phase of operation of the shock absorber to regulate ow of the liquid so as properly to snub the rebound action, and in this connection, another special and important object of the present invention is to provide simple, practical means directly actuated by the ow and the pressure of the liquid produced as a result of the compression shock to actuate the metering pin to its starting or set position, whereby the rebound control is precisely proportional to the compression shock from which the rebound action emanates.

The present shock absorber includes a liquid reservoir and metering pin means operable normally by pressure of the liquid in the shock absorber generated by compression shocks imposed upon the shock absorber to regulate flow of liquid `from the cylinder of the shock absorber to said reservoir for the purpose of snubbing or absorbing the compression shocks. If a vehicle upon which the shock absorber is used is well sprung and its body is substantially fully loaded, or overloaded, it will tend easily to bottom in the absence of some means to actuate the metering pin means positively in a manner to control ow of the liquid to prevent the bottominsl Accordingly, another special and important 0bject of the present invention is to provide simple, practical means operable upon the final portion of compression movement of the shock absorber to positively actuate said metering pin means to control ow of liquid from the cylinder to the reservoir in a manner to prevent said bottoming.

With the foregoing and other objects in view, whichv will become more fully apparent as the nature of the invention is better understood, the same consists in a hydraulic shock absorber of the type mentioned embodying the novel features of construction, combination and arrangement of parts as will be hereinafter more fully described, illustrated in the accompanying drawings, and dened in the appended claims.

In the accompanying drawings, wherein like characters of reference denote corresponding parts in related views:

Figure 1 is a central, longitudinal section through a shock absorber constructed in accordance with one practical embodiment of the invention.

Figure 2 is an enlarged central, longitudinal section through the piston thereof showing the piston valve elements in their normal positions.

Figure 3 is an enlarged central, longitudinal section through the valve means for controlling flow of liquid between the cylinder and the reservoir of the sho-ck absorber.

Figure 4 is a view similar to Fig. 1 showing the piston valve elements in positions as produced by a compression shock imposed upon the shock absorber.

Figure 5 is a cross section on the line 5-5 of Fig. 4.

Figure 6 is a cross section on the line 6-6 of Fig. 3.

Figure 7 is an enlarged section on the line 1 1 of Fig. 2.

Figure 8 is a view similar to Fig. 2 illustrating an alternative form of the piston valve means.

Figure 9 is a fragmentary section through and at right angles to the Fig. 8 structure.

Figure 10 is a View similar to Figs. 2 and 8 illustrating another alternative form of the piston valve means; and

Figure 11 is a view similar to Fig. 3 illustrating positive actuating means for the metering pin means which controls flow of liquid from the cylinder to the reservoir of the shock absorber.

Referring to the drawings in detail, it will be ner.

-ing said port.

fdiskv I8`and said metering-pin constantly is'lurged observed that the present shock absorber is of the cylinder and piston or strut type descrbed in my aforementioned prior patents and includes a cylinder Ill and a piston II for connection with any desired pair of relatively movable elements such, for example, as the axle and the chassis or body of a motor vehicle.

While the present shock absorber may be disposed for operation either vertically or horizontally or at any desired inclination, it will be assumed, for'purposes of simplifyingthe present description, that it is disposed vertically withits cylinder IU and its piston II connected to tlie axle and the chassis or body, respectively, ,of ia vehicle of the type in which the body is yieldably supported upon the axle by suitable springs.

Concentric with and surrounding "the :cylinder I in spaced relationship thereto is a tube I2, while closing the upper and the lower ends of' said cylinder and tube and holding them in their spaced apart relationship, are rupper land :lower heads I3 and I4,'respectively. These heads may be of 'any suitable construction and may be -mounted in closing relationship'to the-ends-of 'the cylinder II] and the tube'I2 in -any suitable man- For example, vthe lower head I4.may 'comprise a main body portion I5 welded, threaded or Sotherwise suitably fastened to the lower end of the tube I2,'and a separate plug elementi! B'superimposed upon said main body portion and having the lower end of the cylinder ID seated thereon, while the upper head' I3 may be of like construction or may Vconsist of only a single element welded, threadedor otherwise suitablyffastene'dto the upper end ofthe tube I2 and suitably engaged vwith the upper end ofthe cylinder I0. In any event, the piston I I divdes'the cylinder I0 yinto upper and lower pressure chambers 'designatedas a, and b, respectively, while the space-between the cylinder Ill andthe tube I2 constitutes a liquid "said reservoir'to said pressure chamber under-the control of a check valve I8 in the form o'ffaidi'sk which opens upwardly and closes downwardly lupon a seat surrounding rs'aid port I1.

` Suitable spring means such, for example, as spring 'ngers I9 projecting `inwardlyvfrom'a :ring 2`Umounted 1in the upper part of the plug element I-6 andenmgaged with the top of the check valve I8, ten'd constantly to urge said valve downwardly'upo'n its seat to close the port l1.

Formed centrally through'the-'checkvalve'disk v IB is a port 2| which r'affords communication be tween the pressure chamber b and thereservoir y:c under the control of Ua metering 'pin 22lwhich extends through said port and is provided with Ian upwardly' facing, preferably upwardlyI tapered shoulder 23 for cooperation with a seat surround- Saidf portv is opened byi downward movement of said metering pin relative lt'oftrie upwardlyI toward 'aposition closing vsaid fport'b'y suitable spring means such, for examplef'as'spring fingers 24 which are'engaged with `thetop of the Adisk I8 and which-project outwardlyfroma ring `25 disposed beneatha pin 26 extending through said metering pin. 4

Formed preferably vas an inte'gral'part of the 4 28 which is disposed within said well whereby a dash-pot is afforded to cushion, retard, and smooth out downward movements of said metering pin. The piston formation 23 is of slightly lesser diameter than the internal diameter of the well 21 to afford a clearance space 29 for restricted iiow of liquid from the well space beneath said piston formation to and through the open top of said well. In the metering pin v22 is an axial bore 30 in the lower end portion of which is disposed a ow control valve in the form of pin 3l which, like said lmetering pin 22, is provided with a piston formation '32 disposed within the well 21 to afford a dashfpot to cushion, retard and smooth out down- -ward movements thereof.

In thefpistonformation 32 may be one or more narrow slits 33 for restricted flow of liquid from the well space beneath said piston formation to the well space thereabove, or, if desired, said -lpiston-formation 32 may be of slightly lesserdiameter than the internal diameter of the wel1i21 `for this purpose.

Suitable spring means such, for example, as-f'a helical `spring 34 interposed between the bottom of the well 21 and the piston formation v32, Ais lprovided to urge the iiow control valve A'til con- ."-stantly upwardly.

The ow control valve 3| yis downwardly 'rnovable relative to the metering vpin 22 under lcertain conditions by pressure of liquid generated fin the pressure chamber b acting upon its upper fend, 4and its upper end portion is upwardly ltap- I"eredas indicated at 35 so that as it moves downliquid from'the pressure chamber b downwardly Jthrough the bore 30 of the metering pin 22 to the well space beneath the piston formation 28 of said meteringy pin' 22.

l,Atfthe top of the piston II is a wall 36 having therein a central bore in which is threaded the V@lower end portion of a piston rod 31 which ex- "ten'ds from said vpiston upwardly through the pressure chamber a and through the upper head I3 for connection in any suitable manner with,

fior-example, the chassis or body of a vehicle.

Any suitable means maybe provided for connecting the tube I2 with, for example, the axle "offla vehicle. It thus will be apparent that road V`"conditions which produce compression shocks; "i, e., which cause the vehicle axle and bodyto l'approach each other and compress the vehicle springs, lwill result'in relative inward movement "of the cylinder II! and the piston Il, whilecon- 'ditions which cause the vehicle body and its axle fto move apart will result in relative outward movement of the cylinder Il) and the piston I I.

Referring more particularly to the piston struc- `ture illustrated in Figs. 2, 4, 5 and 7 of the draw- `ings,1it will be observed that the piston II is Yhollow ybelow its top wall 36 and has disposed therein a valve body 38 which is clamped'ber tween-the wall 36 and a valve seat ring 39 which is threaded into the lower end portion of said piston.

The valve body 38 is of lesser diameter than Vthe internal diameter of the portion of the pislton II in which itis disposed and may be held centered or coaxial with said piston in any suitable manner, as, for example, by means of exterior lugs 49 thereon engaging the interior face ofsaid piston. In any event, there is a space'l Vbetween said valve body and the side wall of the tlpisto'niil Irfand there are holes 42 in' the piston top wall 36 through which said space 4| is in constant communication with the pressure chamber a. Moreover, said space 4I is in one-Way communication with the pressure chamber b through a large central port 43 in the valve seat ring 39 under the control of an upwardly opening, downwardly closing check valve 44 cooperating with a seat 45 surrounding said port 43, and in opposite-way communication with said pressure chamber b through a port 46 in the lower end of the valve body 38 under the control of a metering pin 41.

. The check valve 44 may be of any suitable type and is illustrated as comprising a marginally free, iiexible ring mounted at its inner edge upon the lower portion of the valve body 38.

The port 46 Opens into a chamber d in the lower end portion of the valve body 38 and this chamber is in communication, above the check valve 44, with the space 4I through ducts 48 in the said lower end portion of said valve body.

The metering pin 41 is disposed coaxially with respect to the piston I I and its lower end portion is in the form of a head 49 including an upper cylindrical portion 5U of substantially the same diameter as the port 46, and a portion 5I directly therebelow of progressively decreasing diameter upwardly, both for cooperation with said port 46 in which said head is disposed.

In the upper portion of the valve body 38 is a dash-pot well 53, while in the intermediate portion of said valve body is an axial bore 54 which extends between the top of the chamber d and the bottom of said dash-pot well.

Directly above its head 49 the metering pin 41 includes a portion 55 which neatly fits the bore 54, while above said portion 55 said metering pin includes a portion 56 of reduced diameter which extends through and neatly ts a check valve ring 51 of rubber-like material which preferably is of circular cross section.

The ring 51 seats downwardly upon a preferably downwardly tapering seat 58 at theupper end of the bore '54 and is retained normally in engagement with said seat by suitable spring means such, for example, as a ring 59 overlying said ring 51 and having spring fingers 60 projecting therefrom into a groove 6I in the side wall of the dash-pot well 53.

Above its portion 56 the metering pin 41 is in the form of a stem 62 of smaller diameter than said portion 56 whereby an upwardly facing shoulder 63 is formed at the junction of said stem with said portion 56.

In the dash-pot well 53 is a plunger 64 which includes a guide portion 65 extending upwardly into a bore 66 in the lower end of the piston rod 31. The guide portion 65 is of closed-top, open bottom, hollow form and the stem portion 62 of the metering pin 41 extends upwardly therethrough and has threaded connection therewith at its top, whereby the spaced relationship between the head 49 of said metering pin and the dash-pot plunger 64 may be varied. A locknut 61 threaded on the upper end of the stem portion 62 for cooperation with the top of the guide portion 6-5 affords a means of maintaining any desired threaded adjustment between the metering pin 41 and the dash-pot plunger 64.

Between the top of the guide portion 65 of the dash-pot plunger 64 and the top of the bore 66 in the piston rod 31 is interposed an expansion helical spring 68 which tends constantly to urge the dash-pot plunger 64 and the metering pin 41 downwardly, while between the closed top of said guide portion and a ring 69 which no1 mally is seated upon the ring 59, is interposed a somewhat lighter helical expansion spring 10 which acts through said rings 69 and 59 to normally urge the check valve ring 51 downwardly upon its seat 58. Suitable means preferably is provided to prevent over-compression of the check valve ring 51 by the springs 68 and 18, this means comprising, for example, downturned fingers 1I on the ring 59 engageable with the bottom wall of the dash-pot cylinder 53.

In the lower portion of the metering pin 41 is a longitudinal bore 12 which opens through the bottom of said metering pin and which, at or near its top, is in communication with the bore 54 in the valve body 38 through a lateral hole 13 in said metering pin adjacent to the bottom of its reduced portion 58, while in the outer face of said reduced portion 56 and extending from the upper end thereof downwardly to a point near said hole 13 is a liquid metering groove 'I4 of progressively decreasing cross sectional area downwardly.

In the top of the valve body 38 are suitable openings 15 through which the dash-pot cylinder 53, above the plunger 64, is in communication with the openings 42 and hence with the upper pressure chamber a.

A packing ring 1-6 surrounds the piston |I and operates in accordance the teachings of my afore said patents to prevent leakage of liquid around the outside of Said piston between the pressure chambers a and b.

Under normal conditions the piston I| is disposed approxirnately midway between the ends of the cylinder I8 and the piston parts have relative positions substantially as shown in Fig. 2 of the drawings. That is to say, the plunger 64 and the metering pin 41 are in their lowermost positions; the upper cylindrical portion 5I) of the head 49 of said metering pin is disposed in the part 48; the check valve ring 51 is seated upon its seat 58; the upper portion of greatest cross sectional area of the groove 14 of the metering pin 41 is disposed in the central horizontal plane or portion of least internal diameter of said check valve ring 51, and the check valve 44 is closed.

Also under normal conditions, the check valve disk I8 is closed; the metering pin 22 is in its uppermost position closing the central port 2| in said check valve disk, and the metering pin 3| is in its uppermost position with the cylindrical portion thereof below its tapered upper end 35 disposed in the bore 30 of the metering pin 22.

Both of the pressure chambers a and b as well as the various spaces in the piston I and the lower head I4 are charged with liquid and a suitable reserve quantity of liquid is contained in the reservoir c.

As in the case of my prior patents referred to, the present shock absorber has vfour distinct phases of operation; viz., (l) compression above normal, as when an obstruction in a roadway is encountered and the vehicle spring is compressed with consequent inward movement of the cylinder I0 and the piston I relative to each other from their normal positions; (2) rebound above normal, or relative outward movement of the cylinder II] and the piston II from their compression above norma status; (3) rebound below normal, as when a depression in a roadway is encountered and the vehicle spring is distended with consequent outward movement of the cylinder I0 and the piston II relative to each other from their normal positions; and (4) compression below normal or relative inward movement '37 -o'f the cylinder |83 and the 'piston -`|f| from their lrebourid below normal relative positions.

As an obstruction in va roadway is encountered and the compression above normal phase "of op- :eration takes place with consequentinward movement of the cylinder Ylll and the piston relative to each other, the liquid in the pressure chamber b is subjected to increasing pressure 'with the `result that the piston check valve E4 is'opened and fthe pressure partly is relieved by iiow of some of the liquid from the lower 'pressure cha-mber b through the piston to thel upper pressure fchamber a. Since, however, due to 'the presence of the piston rod 31 in the upper pressure Chambord,

said upper pressure chamber cannot -ac'comino,-v

date all of the liquid which seeks to escape from the lower pressure chamber b, the lconsequent rising pressure in the lower pressure chamber fb acts on the upper ends of themetering pins 22 and 3| and forces them downwardly as a unit, with the result that the port 2| -in the check valve disk I8 is opened .for flow vof liquid from fthe pressure chamber b to the reservoir Yc.

It will be understood, of course, that the present shock absorber may be of `different sizes orcapacities for use in connection with diierent vehicles or other spring suspensions. In `this connect-ion, the average spring will in itself yfunction satis-factorily to absorb all minor compression shocks to vwhich it may be subjected. In other words, for shocks which produce compression 'of a spring not exceeding approximately the initial onedialf `part of its total compressive movement, it is unnecessary and, in fact, even undesirable 'to material-ly snub the spring action. Accordingly,'in any given installation of the present shock absorber, 'the effective area of the port -`2i and the strength `of the spring 24 are such'as to permit the necessary discharge of liquid from the pressure rchamber b to the reservoir c so that the-shock absorber does not act materially to resist compression oit-he vehicle spring within approximately tl-ie initial ione-half portion oiits compressive movement.

The metering pin 22 readily opens to permit discharge of the liquid because the relatively low` pressure and velocity ofthe liquid does 'notcause -said metering pin to move downwardly-so rapidly as to cause the liquid beneath lthe disks '8 -tfo choke the clearance'space 429 in escaping from the Wardly relative to the meteringpin -22 until the tapered upper end 35 of said flow control 'pin extends more or less lbelow vthe bottom of 'sa-id metering pin, depending upon the pressure generated. Liquid then lflows from Ihe pressure `chamber b downwardly through the bore `3|) lof the metering pin 22 beneath `the disk 23v of 'sa'id metering pin and, because of its velocity, more or less chokes the clearance space 29. Because of the greater area of the disk 2B, upon which the pressure of the liquid acts upwardly, than of the portion of the metering pin y22 upon which the pressure of the liquid acts downwardly, said metering pin is forced upwardly and thereby decreases the effective area of the port 2|. As 'a result, flow of liquid from the pressure chamber b through said port -2| is retarded vand 1thereby therpress'ure in the chamber b is'r's'aus'ed 'to rise with consequent 'increase 'in the 'compression resistance *of the shock absorber.

ABeca-use the ilow control pin 3| isv itself dash- 'p'ot'ted and thereby acts vtocause flow of tli'e vliquid beneath 'the disk 28 to be of substantially -constant volume valueconsistent with the ampliltude of compression of the vehicle spring, in'- drease Vin compression resistance of the shock absorber beyond the desired value and as might r'esullt 'trom too 4rapid downward movemen'tf'of T:said vflow cntrolipin in any given instance, Pis

effectively avoided.

Obviously, v4since 'the ldash-pot 4well I21 is y"char'ged lby thelve'rfy action which is to be con'- trolled, there can never be an absence yof ninstantaneous control regardless of the speed of `-4`the jaction. Moreover, the Vcontrol is highl'yadrlv-alz'it'ageousl'y,'directly proportional to the action.

l -During the ccmpressionabo've normal Yphase A'of 'operation of the shock absorber, vthe pressure generated in the compression chamber b results -in yiiow of liquid yffrom'said pressure chamber up- 'wardlythrough the bore 12'and the hole 13 rin "th'e meter-'ing kpin 41 into the bore 54 -of the valve body 38 beneath the check valve ring l51. Asfa result, said check valve ring is vlifted rom'fits seat and liquid is admitted to the dash-pot cylinder 153 beneath'the plunger 64, thereby causing said plunger and the'metering'pin 4-1 to be more or less raised, depending'upon the pressure generated, until the tapered portion 52 of the lhead vfor said metering pin is disposed in or above the port -45 and the lower constricted portion of th'e groove 14 of said 'pin is 'disposed' in the central, 4horizontal plane of the check valve ring 51, `all Vas shown by way of example in Fig. 4 of the drawings.

As the rebound above normal phase of 'op- "eration 'of the `shock absorber 'occurs following its'described compression above normal phase i of operation, with'c'onsequent outward movement ofthe cylinder V||J andthe piston relative to "each other, the liquid in the chamber a is subiected togpressur/e, the check valve 44 andthe check valve ring-51 -become seated and the pressure of the liquid acting downwardly upon the plunger v64 'and the metering pin 41 assisted "by the Lforce vof "the spring A"58, Icause said metering pin to move downwardly at "a rate governed on the one hand by the rebound pressure generated and, on the other hand, by the effective area f the groove 14 through which liquid from the "dash-pot cylinder 53 passes in itsreturn o'W to the pressure chamber b. v

The 'eiiective area of the port Iltis, of course, 'relatively small at the moment of initiation "of lthe vrebound 'above normal phase of operation, 'but increases as the metering pin 41 moves downwardly. rDownward or return movement Iof ythe metering pin l'fl' is governed by the grooved through which 'liquid escapes from the dash-.pot "cylinder :53 in 'its `return flow to the pressure chamber b land is maintained at a substantially 'constant rate -because of increase in the effec'- "tive cross sectional "ar'eaof the v'groove'lll as the V'p'r'ess'ilre in the chamber 'o decreases. 'The por- 'tion 5| "of the metering pin head permits in- 'creasedflow of liquid from thepre'ssure chamber a to the pressure chamber h as the'pressure in the "pressure chamber "la decreases and may be `designedto permit such ow at a rate to aord vmost 'desirable snubbing or 'checking of the l'rebound action. Obviously, since the metering pi'n j`|1V is 'raised to 'a set 'position by theaction which :stores `the "rebound energy 'in the vehicle spring, control of the rebound in proportion to the energy to be snubbed or checked is assured.

Since, due to the presence of the piston rod 31 in the pressure chamber a, not enough liquid is delivered from said chamber to the chamber b to maintain the latter chamber filled during outward movement of the cylinder l0 and the piston Il relative to each other, the additional liquid required to maintain said chamber b i'llled is drawn from the reservoir c through the port I1.

Since the degree of rebound control is governed by the amount of charging the dash-pot well 53 receives, over-control on higher frequency, low amplitude washboard roads are avoided due to the hole 13 being of such small size as not to admit liquid in sufficient quantities to said dashpot cylinder to appreciably charge the same Within the brief periods of time during which any such charging might otherwise occur. Therefore, the main control port 46 will not be reduced in effective area to the point where a bound down. harsh ride might result. On the other hand, on low frequency pitching, where there are longer periods of time for ow of liquid through the hole 13 into the dash-pot cylinder 53 and consequent raising of the metering pin 41, the effective area of the main control port 46 will be reduced considerably with the result of effectively damping out the pitching.

The rebound below normal phase of operation of the shock absorber occurs when, for example, a vehicle wheel encounters a hole in a roadway. Upon such an occurrence, the vehicle spring is distended and the cylinder I0 and the piston Il are moved outwardly relative to each other from their normal relative positions. Pressure thereby is generated in the upper compres sion chamber a and acts downwardly upon the plunger 64. The spring 10 yields readily under comparatively low pressure generated in the pressure chamber a and acting downwardly upon the plunger 64, and in the normal position of the metering pin 41 the effective cross sectional area of the groove 14 is comparatively large so that free flow of liquid from the dash-pot well 53 below the plunger 64 is permitted. Consequently, under comparatively low pressure generated in the pressure chamber a, the metering pin 41 is moved downwardly the necessary small amount to move the portion 50 of the head of said metering pin out of the port 46. Opening of said port 45 permits dumping of liquid from the pressure chamber a into'the pressure chamber b and as a consequence the vehicle wheel is permitted to drop substantially freely into the hole in the roadway without disturbing the equilibrium of the vehicle body.

The compression below normal phase of operation of the shock absorber occurs following the rebound below normal phase of operation as the vehicle wheel rides out of a hole in a roadway and equilibrium is sought to be established between the energy exerted by the vehicle body downwardly against the force of the vehicle spring exerted upwardly. The loss of energy of the vehicle spring during the rebound below normal phase of operation of the shock absorber and needed to establish a condition of equilibrium, is supplied by the resistance to inward movement of the cylinder Ill and the piston H relative to each other as heretofore eX- plained in connection with the compression above normal phaseof operation of the shock absorber.

With a well sprung vehicle substantially fully 10 loaded, or overloaded, bottoming will tend to occur in some instances under conditions which produce the compression above normal phase of operation of the shock above. To avoid this, means may be provided to insure positive downward movement of the flow control valve 3l a sufcient amount at a time suiciently in advance of the bottoming to permit sumcient liquid to flow through the metering pin 22 beneath the disk 28 thereof to urge said metering pin upwardly the necessary amount to sufhciently check the now through the part 2| to prevent the said bottoming.' Such means may comprise any suitable member movable downwardly by the piston H and effective at the proper time upon downward movement thereof to positively move the flow control valve 3| to tis limit of ldownward movement as determined by any suitable stop means such, for example, as the bottom of the well 21 with which the bottom of said valve is engageable. In the present instance said means is illustrated in Fig, 11 of the drawings as comprising a pin 11 engaged at its bottom with the top of the flow control valve 3|' and extending upwardly into the cylinder I0 for engagement and downward movement by the piston Il upon the occurrence of a certain amount of inward movement of such piston relative to the cylinder Hl. Preferably the upper end portion of said pin 11 is of helical spring form as indicated at 18 so that said pin is brought into action gradually rather than abruptly.

Referring to Figs. 8 and 9 of the drawings, it will be observed that the construction therein illustrated differs from the Fig. 2 construction primarily in that the metering pin 41 i-s not anchored to the plunger 64a, but is yieldably mounted with respect thereto. In other words, the plunger 64a is provided with a bottom abutment 1S, the metering pin 41a is provided with a top abutment 80, and the spring 10a is interposed between said abutments. As a result the metering pin 41a obviously is permitted to move longitudinally relative to the plunger 64a. Accordingly, should the pressure developed in the chamber a during the rebound above normal phase of operation of the shock absorber become such as to accelerate downward movement of the plunger 64a to an extent such as to momentarily cause the groove 14a to become choked with liquid and thus halt the downward movement of said plunger, downward movement of the metering pin 41a may continue with the result of increasing the effective area of the port 46a, and affording the equivalent of a blowdrops into a hole in a roadway, the metering pin 41a is movable downwardly resisted only by the spring 10a and thus the pori-l 46a may readily open to permit `dumping of liquid from the charnber a into the chamber b and consequent free i dropping of the vehicle wheel into the hole.

In short, -the Figs. 8 and 9 construction accomplishes the two very desirable functions of affording a constant resistance to unloading movement of the metering pin 41a during rebound below normal phases of operation of the ascenso;

11 shock. absorber, and a varying or pop-off. refsistance to said. metering pin during. rebound above normal. phases. of operations of the shock absorber.

In, other respects, the Figs. 8 and 9 construe..- tionv and mode of. operation are generally the. same as the. Eig. 2 construction. However, n.- stead of the. valve. body 38a being held positioned' inthe piston lla. by engagement of the` top ofi the valve seat ring 39a. with. thev lugs 4.011 of said valve. body, said valvev body is held positioned.

by the. seat 45a of said. valve seat ring operatring through the check. valve 44a to engageI be.- neath a ange 8l of said valve body. The under faceof said flange. 8l is of convex contour to permit the check valve lilla to open.

Referring to Fig. 10 of the drawings, it WilL be observed that the construction therein illustrated is generally the same as the Fig. 2 construction, excepty that the. valve body 38h is screwed into the piston l lb andthe check valve 44h is in the. form of a flange extending laterally outward, from a cuplike member 82 whichis slidably mounted on the lower end. portion of said. valve body and which has in its lower end. portion the chamber Mb and the port dbb with which the head @Bb of the metering pin Mb cooperates. A coil spring 83 between the check valve flange Mb and the bottom of the valvebody 33h urges said check valve ilange normally to its seat. When said check valve Mb is seated...

the cup-like member 82 is, of course, disposed:

and described, the improvements are capable ofi' embodiment in specifically different structures within the spirit andfscopeof the invention as denedv in the appended claims.

, I claim: Y

1. In a hydraulic shock absorbena cylinder., a piston reciprocable therein, a liquid reservoir, a head closing one end of said cylinder andhaving therein a port aiiording communication'between' said end of said cylinder and said reservoir', a check valve controllingv said port and having therein an orifice aiording communication between said end of said cylinder and said reservoir, a metering pin extending through said orice and inwardly movable to close and outwardly movable to open the same, yieldable means tending constantly to move said meter-- ing pin inwardly to close said orice, the innerend of said pin being exposed within the cylinp-A der for subjection to liquid pressure to urge". said pin outwardly' and thus open said orifice. said head having a well and said pinhaving: a piston portion disposed in said well to providea dash-pot to resist outward movementrof' said pin, and means including a yieldably closed valve openable by the pressure of the liquid in said end ofv said `cylinder to admit a portion of the liquid to said well outwardlyv of the piston por- 70 tion of said pin to vurge said pin inwardly.

2. In a hydraulic shock absorber, a cylinder,

a.` piston. reciprocable therein, a, liquid. reservoir.,v a. head closing. one. end of. said. cylinder and. havtherein aport aording communicationA between saidv end.. of said cylinder and. said res ervoir,I a; metering pin. extending. through saidv port and. inwardly movable. to close and out wardly movable to open thesame, yieldable means tending constantly to urgesaid. pin inwardly to ay port-closing. position, the. inner end of. said pin being exposedv withinv the said. end of, said; cylinder for subjection to liquid pressure to urge said. pinv outwardly and. thus open saidy port said head. having a well and said pin having. a. piston portion. disposed in. said well to provide, a dash-pot to resist. outward movement of. said pin, means including a., yieldably closed valve. openable by the pressure of the liquid to admitA a..porti`on,of the liquid to said. well outwardly of the piston portion. of said pin to urge. Said. pin, inwardly, andv mechanical means operable. by said, piston.l duringvr the latter portion of the4 compressioni, above normal phase. of operation. of. the shoclli.v absorber to positively opensaid valve..

3. In a hydraulic shock absorber, acylinder, a. piston reciprocable therein, a/liquid` reservoiis., a head. closing one endlof.- said cylinder and. having thereirra port affording communication. be.- tween said.' end of said. cylinder and said res.- ervoir, a metering pin extending. through said. port, and inwardly movable. to close and outwardly movable to openlthe same, yieldable means, tending constantly to urge said' pin inwardly to. a port-closing position.. the inner end of said pin. being, exposed within the said end of said cylinder for subjection to liquid pressure to urge said pin outwardly and thus open said port, saldiA headv having a well` and saidpin having a piston. portion disposed in said Well to. provide a dashpot to resist outward movementA of said pin., means including a yieldably closed valve openable by' the pressure ofthe liquid to admitv a portion.l of the liquid to said well. outwardly of. the piston portion of4 said. pin to urgev said' pin. inwardly; andla valve actuating pin engaged with said valve and extending into' said end of said..

cylinder for engagement by said piston during. the latter portion of the compression above normal. phase of operation of the shock. absorber'- toV positively open said valve.

4. A shock` absorber as set forth in. claim 3v ini which the inner end portion of the valve actuating pin is in the form vof a helical spring.

5. A hydraulic shock absorber as set forth in claimI 1' in which the metering pin is provided with an. axial. bore andthe yieldably closed valve is' in the form of" a pin disposed in said bore and having its'inner end portion inwardly tapered for outward movement beyond the outer end of said meteringr pin to progressively Aopen the bore of said metering pin for flow of liquid therethrough from' the: cylinder to the well" in which said.

metering.' pjin' is' disposed.

. NEvIN s'. FOCHT.

REFERENCES CITED The1- following references are of record in the ille oi'. this patent:

UNITED STATES PATENTS Number Name Date 2,111,192. Padgett Mar. 15, 1938 2409349 Focht Oct. 151946 

